Heat treating system



Aug. 1, 1939. J. w. HARscH HEAT TREATING SYSTEI Filed Jan. 12, 1958 5 Sheets-Sheet l S SN ug. 1, 1939. '.1. w. HARscH Ik -2,168,028A

HEAT TREATING sYsTEu Filed J'n. 12, 19:58 5 sheets-snaai 5 UNITED'. STATssAPATi-:NT

ol-Fics 'maar TREATING SYSTEM .reim w. namen, Gwynedd, Pa., assigner to Leeds Pa.,

Northrop Company, Philadelphia, a corporation of Pennsylvania Application January 12, 193s, serial N0. 184,554

11Claim`s.

My invention relates to heat-treating systems and particularly to furnaces suited for carburizing or other heat-treating processes involving highftemperature application of suitable chemically-active gas to work In accordance with one. the retort for containing pieces under treatment.

aspect of my invention,

the work pieces remains in the furnace during loading, treatment, and unloading,and the sealing venting ingress into the arrangement, for pre` retort of atmospheric air or leakage from the heatingchamber of the lfurnace, or leakage from the retort of'gas therem, is constructed to'allow the retort to expand and contract, withoutvappreciable restriction by the retort cover.' the seal parts of the furnace, and the eillcacy of the seal.

structure or stationary without impairment of Further in accordance with 'my invention, sealing of the retort such as ne sand having is effected by fluidic material, suitable, generally low.

angle of repose, and suitable bailles are'provided to prevent entrainment o ing material by the retort f particles of the sealatmosphere, especially when forcibly stirred or circulated.

Preferably, a floating member of the seal structure additionally serves as an inner cover or wall which more or less completely closes the heating chamber when the' outer moved, with effect to cons cessive runsof the furnace.

resides in the features of construction, combination My invention further hereinafter described and For an understanding of my invention and for illustration of various or retort cover is reerve heat between sucand arrangement claimed.

forms thereof, reference is n to be hadto the vaccompanying drawings, in

which: n

Fig. l is a front elevational View, mainly in sec-v tion, of a heat-treating furnace:

Fig. la is 'a detail ing shown in Fig. 1; Fig. 1b is a detail view,

view of a sealing ring` mounton enlarged scale, of a part of seal structure shown in Figs. 1 and la;

A Fig. 1c is a detail view,

largely in section, of a fan shaft seal shown in Fig. 1,

2 is a front elevational view, largely in section, of a heat-treating furnace utilizing a modied seal construction; Fig. 2a is a sectional seal structure shownin viewA on enlargedV scale of l Fis. 2;

Figs. 2b', 2c and 2d are detailsectional views showing other sealing arrangements;

Fig.' 3 is a fragmentary, largely in section, of 'a showing a modified form front elevational view, heatftreating furnace of heater construction;

metal base plate I Fig. 4, in general similar to Fig. 2, illustrates a different fan construction and modified form -of agent-introducing device;

Fig. 5 is ahorizontal sectional view taken on line5-5ofFig.4; v 5

Fig. '6 is a vertical sectional view, partly in elevation, of a furnace heated bycombustion; Y

Fig. 7 is a plan view of the fan and associated vane construction of Fig. 6;

- Fig. 8 is a front elevational view, tion, of Fig. 7,' A

Fig.'9 is a sectional view, with electrical diagram, showing an arrangement for igniting exhausted treating gases.

' Referring to Fig. 1,l the furnace F comprises a 15 supportedat suitable height the standards `or legs 2. The member 3 suitably attached to I, as byscrews 4 andangular above the floor by outer metal shell the base member members; 5, surrounds the layers of bricks 6,16 of 20 suitable heat insulating material such as diatoma cecus earth brick and' a layer of bricks preferably of suitable refractory material, such as ie-- brick, which line or form the side-wall structure of the heating chamber H of the furnace. AThe 25 bottom wall of the heating chamber and of the 'furnace comprises a plate 8 of suitable refractory material, which rests upon the plate 9 of suitable heat-insulating material which, in turn,1is supported by the base plate I. l The channel member Il in the base of the furnace is adapted to receive the lower end of a tubular retort member. II, preferably or generally of circular cross-sectie which, -in the construction specically illustrated, is comprised of several short sections secured, as by welding, to each other.' Preferably the retort, as well as other metal parts of the furnace interior, is of nickel-chromium alloy or the like. Near its lower' end the retort is provided with an inwardly di- 40 rected ange I2 which rests-upon the upper inner Normally, however.`the retort remains `in the furnace during loading,

treatment, and unloading ofthe work.

The channel member I 0 inthe base of thfur# l Y nace holds a suitable quantity ofsealing material which, for the particular purposes herein specif- '55 partly in secl10 lematerialcapobleofmgnm. peraturesandwinthesenseitiacapable 'odowingabouttheloweredgeofretort il during andcontractionotheretortmdupon insertion into or from channel Il should have a low angle of repose; alternatively, the iiuic sealing material maybeofanyliquid pableorfmaintadningmteerif0ftbesealunderthe,physicsl mode of heat-treatment.

Fromtheexte'rioroftheretorhneartheupper end thereof, proiect several pairs of abutments il for en the members l! projecting inwardly from the channel member W which normallysinround'stheretort it. AslshmminFlss. ltr-and lb,thechannel lisretainedintheposltionshowninFlg. lbykeys11,eachotwhich extends vertically between a pair of abutments M onthe retortand apair of abutments i5 on thechannel, the wire or ootterpin Il preventing the key from dropping from place, By this construction, the retort and the channel mem ber I6 may move relatively with respect to each other during their heating and cooling without production of due to 'differences in' expansion and contraction of these two members. The channel member li is mounted upon or removed from the retort while the retort is out of the furnace. To remove the channel ii, thekeys I1 and their retaining wires t8 are rst removed: then channel I6 is rotated sufllci'ently to eflect disengagement between the pairs of lugs M on the retcirt and pairs oi lugs I 5 on the channel to allow the channel to drop clear of the retort. To position a channel member I6 on the retort the operations are performed in reverse sequence.

The channel li provides support for another body of sealing material which is preferably of the same iluidic character as that retained by channel I0. When channel IS is in position in the furnace, Figs. l and 1a, it receives the outwardly and downwardly directed flange i! at the upper end of the retort, and also receives the. lower end of the hanged member 2li depending. from the cover 2l Vwhich may bei raised with respect to the supporting member 22 pivotally mounted on one side of the furnace to afford access to the furnace retort forA loading.

By the construction described the retort Il, the channel member i5, and the cover plate 2l are each free to move with respect to the other and to the main body of the furnace, when subjected to thermal stresses arising from their expansion and contraction during heating and cooling of the furnace, without any impairment of the seals at either end of the retort whose purpose is to prevent leakage into the retort from the heating chamber or from outer atmosphere, and to prevent leakage from the retort to the heating chamber or to atmosphere. 'I'he absence oi any rigid connection between the retort and stationary structure of the furnace, between the cover and the retort, and between the cover and stationary structure of the furnace, results inv increased life oi these furnace parts and freedom from breakdown of the seals during a run with consequent adverse eiiect upon the work under treatment.

. bythe packing Y engages the outer periphery Inporticulantbeiioatingmountingofthechannelpermltstheretorttoexpandandcontract withoutrestraintimposedbythechannelorthe eoveriiangelt.

Forsupportingtlworkpieceswithintheretort, and to facilitate loading and unloading, there is preferably provided a removable work baskethavingliitngeyesllattheupperend thereof and rovided at the bottom with a grid orgrating 2 which the work pieces.

'Ihelowerendcftheworkbasket insupportedbythe member 2i having several legs 26a which extendthroughthebue' ofthe furnace andrest upontbebase plate l, Thecentralportionof the member VIt is `open and shaped to provide a, duct iromthe ofthe workbaskettothe ian 2l in the base of the retort. The deflection plate 2t which rests upon the bottom of the furnace is suitable curved to direct the atmosphere circulated the retort by the ian toward or from the ian depending upon the. direction of circulation. Preferably, as shown in Fig. l, the direction of circulation is such that the atmosphere in the retort downwardly through the work basket to the fan andthence upwardly around theworkbaskettothetopoftheretort.

Whentheian 2T is oftheblowertypeor ofthe propellertypewith high bladeangle toobtainblower characteristics, the gases swirl about the work basket as theyadvanceoxiallytoward the topofthe retort. Since the deflection plate 2l is of diameter suitably less than the internal diameter of the retort to avoid any restriction of the retort during its contraction, there is tendency for the swirling gases to draw the small particles of sealing material iromtbe channel lll into the treating chamber but this depletion of the seal is precluded by the inwardly directed flange I1 of the retort.

The swirling action of the gases also tends to draw particles of sealing material from the upper channel i6 into the retort but this .is effectively prevented by the small vanes or swirl-breakers 2S depending from the cover plate 20 near its region oi approach to the upper rim of` the retort Il.

The fan 21 is driven at suitably high speed, for example, i800 revolutions per minute/,by the motor 30 suspended from the base plate 'i' of the furnace by the brackets 3l.

The'ian shaft 32 extends loosely through the member Il. mounted in the base of the furnace and, prcIerabLw-as shown, provided with a passage l 'for circulation of water or other cooling liquid.

ring IIT (Figs. l and 1C) of rubber or the like, compressed between the bottom of member 3l and the housing of motor 30 when the latter'is drawn into place by bolts Ila. The upper bearing oi the motor comprises the housing IBI preferably integral with the top cap l!! and mounting brackets 3|. Within the recess IIII of the bearing housing is disposed, at the upper end of the recess, the packing or sealing ring I l I, of suitable material, preferably Duprene or like material, unaffectedv by oil or grease, whose upper edge and outer periphery engage the inside The inner periphery of ring Hl of the upper part of the metal seal member H2 having a. shoulder which engages the lower edge of the packing ring III; the inner diameter of memberill is slightly greater than the diameter of motor shaft 32a. Within a recess of the housing.

thickness somewhat less than the depth of the recess. Between the upper face of ring H3 and At its lower end the member 33 is engagedin the lower face of the 'member Il! is disposed the thrust washer H3 of tending to shorten the the member H2 is disposed a thin metal annular diaphragm H4, specifically copper, the inner edge of which is pressed downwardly -by a plurality of springs H5 disposed in recesses H6 in the upper part of member H2; the outer periphery of -dia phragm H4 is brazed or welded to sealing member I I 2 and the inner periphery thereof is similarly fastened to the thrustring I|3 thus to form a gas-tight'seal. 'I'he lower lapped surface of ring H3 and the upper lapped surface of race |23 rotatable with shaft 32a provide a sliding gastight seal lubricated as described hereinafter. The stationary races I I1., I I8 of the two ball bearings shown lie within the housing |08 below the rings II2 and I |3 and' are held in place by the ring I I 9 held in position by a plurality of bolts |20 which pass downwardly through the housing |08 and which, at their lower ends, ,threadably engage the ring or plate I I9. The rotating race I2I of the lower ball bearing abuts against a shoulder |22 on the motor shaft 32a.

Preferably each of the ball bearings is provided with a thin metal ring |24 secured as by welding to the associated stationary race and extending almost into contact wi grease retainer. The passageway |25 through the housing permits the upper motor bearings to be lled with a suitable lubricant.

Transfer of gases to or from the interior of the 'retort along the fan shaft is prevented by the are disconnectable to facilitate assembly andre- -placement of either the fan or the motor; specifically, the motor 'I shaft 32a is hollow and is provided at its upper end with an internal taper to t the taper of the fan shaft 32.

The space between the outside of the Wall structure of the retort and the inner face of the heating chamber is heated in any suitable manner; in the particular arrangement shown in Fig. 1, the ribbons 34 of suitable resistance material, such as nickel-chromium alloy, are hung from the refractory blocks 1. lining the heating chamber and suitably connected as by conductors 35 to terminals 36 connected to a source of electric current.

Preferably, as shown, there are provided several passages 31 for admitting air at suitably low rate to the lower end of the heating chamber, and at the upper end of the heating chamber the blocks 38 are slightly' spaced from the outside of the channel I6 andffrom the lower side of the cover 2| to afford-for the. heated air an exhaust passage 39 from the heating chamber. Consequently, 'during heatingof the furnace there is movement of hot air about the channel I6 which is effective to minimize differences of temperature in different portions of the channel ber I6.

Since the channel member I6 substantially closes the top'of the annular heating space about Vthe retort even when the main cover 2| is removed for loading or unloading of the retort, the 'heat of the heating chamber is to substantial extent conserved. The air admitted to y the heating chamber by N th the outer periphery of A the corresponding rotating race to serve as a.A

and thus reduce strains life of the channel memf: 31 is also effective to combust any carbonaceous material which may leak into the heating chamber and which otherwise might be deposited on the electrical heating elements and cause trouble by short circuits` or grounds.

For carburizing the pieces in the workbasket, a suitable carburizing agent, for example, fusel oil, dipentine, butane, or natural gas, is fed, preferably at metered rate as by a positive displacement pump P, to the nozzle 40 from which it drops, through the tubular member 4| extending through the cover 2 I, into the upper region of the reaction or treating chamber defined by the retort, the cover member 20 and the seal construction. The carburizing agent when introduced intoload, affording carburization at high rate and without need to supply the agent in such excessive quantity that deposits of soot occur which deposits not only defeat the purpose of high rate of feed of the carburizing agent but also produce non-uniformity of the carburized case upon the work. This and other herein described constructions are suited for performing the methods of carburization described and claimed in my copending application Serial No. 183,618, filed January 6, 1938.

To prevent, when the agent is introduced into the furnace in liquid or vapor phase, impingement of unvaporzed carburizing agent uponthe top of the load, which would tend to produce a cold spot wduring treatment and consequent inferior carporize any of the carburizing agent which reaches it in liquid or vapor form. The vaporized agent is immediatelyentrained by the circulating at- A mosphere and passes therewith downwardly into contact with the work to effect carburization thereof.

I'he pipe 44through the cover of the furnace, provides for continuous` discharge ofthe exhausted treating gases which, for purposes of safety to the operator, are burned as they issue from the pipe 44a, adjacent the open end of which there is preferably provided a continuously operating igniting device 46, for example, a gas llame or an electric spark.

. During operation -of the furnace, and particularly at the region adjacent the lower end of pipe 44, the furnace pressure is slightly higher-than atmospheric; consequently, there is no tendency for atmospheric air to enter the retort through pipe 44. Preferably, the exhaust pipe 4,4 is of substantial diameter, much larger than. pipe 44a 'which is' carried by the cover" for the chamber esj the retort rapidly to assume equality with the at- I mosphere; otherwise, there is tendency for the sealing material in the channel I6' to be sucked into the retort upon lifting of the retortcover or' ber 50. (Fig. 2a).

blown from the channel into the heating chamber during lowering of the retort cover.

Though particularly suited for carburizing,

the furnace of Fig. 1, and of allthe other g- Y ures of drawing, is suited for other modes of heat treatment such as nitriding, bright annealing, tempering, hardening, 'toughening and the like, in which the work, while heated, is subjected to an atmosphere comprising a vapor or gas which obtains -or preserves the desired characteristic composition of the surface, or the surface and subsurface of the work pieces.

When any of the furnaces disclosed are used for carburizing, the agent may be any suitable carbonaceous compound, for example, a hydro.- gen, carbon compound, such as butane, propane, hexane, ethane, or a hydrogen, oxygen, carbon compound such as fusel oil, diethyleneglycol, furfural, diethyleneglycolmonoethylether, or a mixture of such compounds.

Since, in many respects, the furnace construction shown in Fig. 2 is the same as that shown in Fig. 1, thosc elements corresponding to like elements of Fig. 1 are identified by the sameV reference characters; discussion of Fig. 2 is conned to features not present in Fig. 1 or therein appearing in modified form.

The retort Ha of Fig. 2 is provided at its upper end with a channel 49 containing a body of suitable sealing material, preferably of the character previously herein mentioned, and with an inwardly and upwardly directed baffle mem- The stationary channel member |6a at the upper end of the wall structure of the heating chamber contains another body of suitable sealing material, for example, of the fluidic character previously specied. The floating seal member which closes the top of the annular space between the outside of the retort Ila and the inner Wall of the heating chamber H, is provided at its outer edge with a flange 52 received by the sealing material in the channel |611 and near its inner edge is provided with a flange 53 received by the sealing material inV channel 49 at the top of the retort.

Desirable .swirling of the gases about the retort and within the annular heating space is produced or enhanced by the vanes 56 (Fig. '7) attached to the deecton plate 281 in the bottom of the retort.

The ange 54 extending downwardly from the floating seal member 5| between the adjacent faces of members 49 and 50, provides a tortuous path effective to prevent the swirling action of the circulating atmosphere from drawing particles of sealing material from channel 49 into The lower edge of anged member' the retort. 20 of thefurnacevcover 2| is alsoyreceived by the sealing material in the channel Isa.

When the cover 2| is in closed position, the atmosphere within the retort is effectively isolated from the heating chamber and. from the atmospheric air; when the. main cover 2| is moved to its open position for insertion or withdrawal of'work, the floating seal member 5| serves as an aum'liary cover for the annular heating chamber to ccnscerve its heat energy and so reduce the time and ccst of the next run.

The cover. 2|, the floating seal member 5|,

` and the retort are all free to move with respect to each other and. with respect to the stationary structure of the furnace; each of "these members is free to expand and contract during operation of the furnace without distorting ylorvbeing distorted by any of the other members and withmentioned as suitable.

out impairment of the seal construction which remains eifectlve to prevent pollution of the treating atmosphere in the retort by leakage from the heating chamber or fr om the atmosphere external to the furnace.

For feeding carburizingagent to the reaction chamber comprising the retort Ila, the floating seal 5| and the cover 2|, there is provided, in the particular arrangement of Fig. 2, a tank 58 for holding a suitable carburizing liquid, a positive displacement pump P, preferably of the type utilized 4for feeding fuel to a Diesel nozzle, a motor 60 for driving the pump, and a nozzle 6|, preferably of the type used to inject fuel into a Diesel engine, mounted upon thel cover 2| and extending through it to project a jet or spray of carburizing agent into the region above the work basket 23. The hot gases circulating in the reaction chamber entrain and vaporize the introduced carburizing agent, raise it to crack-y ing temperature, and carry it and products of' its dissociation downwardly through the load.

By injecting the fresh carburizing agent immediately above the load, the direction of circulation of the gases being as indicated by the a1"-A rows, it is provided, in accordancewith my aforesaid copending application, --that the primary cracking of the agent shall continue throughout the load, affording high rate of carburization.

In the sealing arrangement shown in Fig. 2b, the annular sealing member 62, whose ilange 63 generally corresponds to the ange 52'of sealing member 5| of Fig. 2,A is connected to the upper end of the retort ||b by the 'annular corrugated that the bellows or expansion member provided by the corrugated member 54a is disposed vertically at the top of the retort ||c instead of substantially horizontally as in Fig. 2b. In both modiilcationathe annular sealing member 52 or 62a andthe retort are oatingly mounted to permit them to move, with respectto the retort during expansion and contraction ofthe seal andthe retort. Boththe seal and the retort are also free to move with respect to theflanged :cover member -20 whose movement, during expansion and contraction, does not restrict the movement of the retort or the sealing inemljr. 'Ihe nature of the sealing material in the flange |6a is such that it ilows upon movement of the flanges y20 and 63 incident to their heating and cooling during operation of the furnace to preserve the ysealed relation of the reaction chamber with respect to-the heating chamber and atmospheric air; specifically, the sealingmaterial may `comprise any Aof the substances herein g inthe modification. shown' `in Fig. 2d, the .top ofthe retort lld, is provided, like the retort o f Fig. '1, with an integral outwardly and downwardly directedflange I9. In this modification,

A -however, the ange is received'jby .the .stationary vchannel |6a at the upper end of the heating To minimize temperature differences in the sealing channel Ilia conducive to its distortion, there are provided extending from the top of the heating chamber adjacent to or in contact with the channel I6a to atmosphere; provision of these passages 39a and inlet passages 3l at the bottom of the heating chamber provide for circulation of air, the heated gases from the annular heating space pass adjacent the sealing channels |6a and so reduce the difference in temperature between the outer and inner portions of the channel. The furnace 'construction shown in Fig. 3 is similar to that of Fig. 2 except for the heater construction. In this modification, the electric heater 34a, is made in two or more sections, each comprising an annular ring of refractory in which are embedded the turns 6l of a helix or spiral of resistance wire. The several heating sections are suitably secured to each other and suspended from the furnace wall without attachment to the retort which, as in all modifications, floats bei tween seals at the bottom and upper ends thereof.

form.

The heat treating system shown in Fig. 4 is substantially the same as that shown in Fig. 2

except there is provided a' perforated vaporizing plate 68 on the under side of the cover 2| below the injection nozzle 6| to prevent impingeinent of unvaporized heat-treating agent uponrthe top ofthe load-in the work basket 23. This plate which performs generally the same function performed by plate 42 of the carburizing agent is introduced in gaseous The fan 21a`shown in this modification is, as clearly appears in Fig. `5, of the blower type; any of the other fan constructions herein shown or described may be substituted therefor. The hot gases discharged by the fan are caused .to swirl,

'as by vanes 56, as they advance axially in the annular space between the outside of the work basket and the inner face of the retort. In the region above the top of the work basket the swirling gases entrain the freshly introduced carburizing agent and move it downwardly through the load. Entrainment of the sealing material by the swirling gases is prevented at the lower end of the retort by flange I2 and at the upper end of the retort by baiiie 50. i

The furnace construction shown in Fig. 6 is substantially the same, as, or similar to that of, the other modifications except for the method of heating the retort. In this modification, the retort is heated to the desired temperature, depending upon the nature of the heat-treatment, by combustion in the annular heating chamber H of the furnace. Specifically, one or more burners B9 supply a suitable combustible mixture, for example, a mixture of fuel gas, or liquid fuel, and air to the bottom of the chamber H'where it is ignited, as by a jump spark device 10. Preferably, the burners 69 enter'the heating chamber .tangentially to cause the burning gases and products of combustion to swirl around the retort as they advance upwardly and axially thereof toward the outlet duct 'Il at or near the upper end of the heating chamber'.

The fan 2lb forforcibly circulating the atmosphere within the reaction chamber into contact with the retort'for absorption of heat for subsequent transfer to the work to raise its temperature to heat-treating temperature, and for equalization of the load, may be cf the having both blower type, shown in Figs. 7 and 8, and propeller characteristics.:

a multiplicity of outlets 39a of internal combustion Fig. 1 may be omitted if'.

temperature throughout the4 5 the fan 21h, Fig. '1, rotates in clockwise direction to cause the gases to swirl in that direction as they advance upwardly in the retort. By reversing .the direction of rotation of the fan, the gases may be caused to circulate in reverse direction in the reaction chamber, i. e., the gases will be forced upwardly through the basket rather than downwardly. It is not desirable, however, that this direction of rotation be utilized, particularly when the furnace is used for carburizing, because primary cracking of the carburizing agent would occur outside of the work zone and result in deposition of soot on the bottom of the load and low carburizing power of the atmosphere surrounding i the top of the load.

`In Fig. 9 there is diagrammatically shown a suitable arrangement for igniting the gas issuing from the retort of any of the carburizing furnaces herein described. such as ordinarily utilized to ignite the charge engines, is screwed intol a metal bracket 13 attached to the outer end of the exhaust pipe 44 of the furnace. One electrode 14 of the spark plug is connected to one terminal of the high tension transformer orY spark coil l whose other terminal is connected to the exhaust pipe 44 electrically connected by bracket 13 to the shell electrode 16 of the spark plug. The switch 'l1 for controlling the primary circuit -ofthe spark coil or transformer 'i5 is preferably having a channel at its upper end for holding a body of iiuidic sealing material, a second channel for holding a second body of iiuidic sealing material disposed about said heating chamber, a floating seal member affording access to the interior of said retort and. for closing the heating chamber space outside of the retort having fianges immersed in said bodies of sealing material, and a cover for said retort having -a iiange received by said second-named body of sealing material and removable for `access to the interior of the retort V,while said sealing member is in place.

2. A heat-treating furnace comprising a heating chamber, a retort remaining within said chamber during loading, treatment, and unloading of the work, channel structure at the upper open end of said retort mounted for movement with respect thereto and containing iiuidic seal- B rieiiy, a spark plug 12,

ing material, and cover structure for closing said '60 furnace including a sealing -flange received by said material to isolate the space within th'e ref tort from the heating chanber space outside the. retort and extending vtherefrom to overlie said heating chamber space outside of the retort.

3. A heat-treating furnace comprising a heating chamber, a retort remaining within said chamber during loading, treatment, and unloading of the work, channel structure loosely supported from the upper open end of the retort and containing uidic sealing material, and cover structure for closing the upper end of said retort having a. sealing ange received by said material and extending beyond the flange to close the heating chamber space outside of the retort.

4. A heat-treating furnace comprising a heating chamber, a retort remaining within said chamber during loading, treatment, and unloading of the work, channel structure within said chamber at the upper open end of the retort and containing fluidic sealing material, and means for closing the upper ends of said chamber andsaid retort comprising cover` structure having a sealing iiange received by said material, extending outwardly to close the heating chamber outside of said retort, and having a central opening substantially corresponding with the open top of the retortand a secondv cover structure movable to open or close the top of the retort while said first cover structure is in place.

5. A heat-treating furnace comprising a heating chamber, a cover for closing said heating chamber, a retort remaining in saidk chamber during loading, treatment, and unloading of the Work, channel structure within said heating chamber loosely mounted at the open upper end of said retort and containing uidic sealing material, and a sealing ange depending from said cover for reception by said materialto complete isolation of said retort when said cover is in position to close said heating chamber.

6. A heat-treating furnace comprising a heating chamber, a retort remaining within said chamber during loading, unloading, and treatment of the work, channel structure at the upper open end of said retort disposed Within said chamber and containing fluidic sealing material, cover structure for closing said chamber, means for isolating the retort atmosphere from the heating chamber space outside of the retort comprising a peripherally continuous ilange received by the sealing material in said channel structure, and

means carried by saidcover structure for feedingI the isolated treating chamber defined by said retort, said cover structure, and said iiange.

'7. A heat-treating furnace comprising a heating chamber, a retort remaining Within said chamber during'loading, 'unloading and treatment of the Work, channel structure at the upper open end of the retort containing fluidic sealing material, cover structure for closing said chamber, structure including a flange received by said sealing material cooperative with said retort and said cover structure for dening an isolated treating chamber, and means for agitating the atmosphere Within said treating chamber comprising fan structure Within the retort.

8. A heat-treating furnace comprising a heating chamber open at its upper end, a channel in the base-of said chamber containing iiuidic sealing material, a fan rotatable above and adjacent said base within the periphery ofsaid channel, a removable tubular retort open at both ends and chamber space outside of said retort and inwardly from said flange to cover the open top of said retort.

9. A heat-treating furnace comprising a heating chamber open at its upper end, a channel in the bottom of said chamber containing fluidic.

sealing material, a fan rotatable above and adjacent said base within the channel outline, a

removable tubular retort open at both ends and whose lower end is received by said channel for closure by the base of said chamber, a second channel containing iiuidic sealing material at the upper end of said retort, and means for closing the upper ends of said chamber and said retort comprising cover structure overlying the heating chamber and retort therein and a sealing ange depending therefrom for reception by said second y channel member to confine to the retort the atmosphere agitated by said fan.

10. A heat-treating furnace comprising a heating chamber open at its upper end, a channel in the bottom of said chamber containing uidic sealing material, a fan rotatable above and adjacent said base Within the channel outline, a tubular retort open at both ends and whose lower end is received by said channel for closure by the base of said chamber, a second channel containing uidic sealing material at the upper end of said retort, and means for closing the upper ends of said chamber and said retort comprising cover structure overlying the heating chamber space outside of the retort having a sealing flange received by said second channel member, and a separate cover structure overlying the top of the retort and removable for loading or unloadingthereof while said first cover structure is in place.

11. A heat-treating furnace comprising a heating chamber, a retort remaining in said chamber leakage.

JOHN W. HARSQH. 

